Direct burner ignition system

ABSTRACT

A fuel igniter element having a resistance value which varies inversely as a function of element temperature is mounted proximate to a burner outlet and is electrically series connected to a substantially constant resistance heater element. The heating element is operable to actuate a thermal valve at a predetermined current heating value to provide fuel to the burner. The series circuit is switchably connected to an electrical power source which when applied heats the igniter element to the fuel ignition temperature of the fuel used. At this temperature, the lowered resistance of the igniter element allows the current flow to increase to the predetermined current value thereby actuating the thermal valve. Upon actuation, the thermal valve allows fuel to flow from the burner which is then ignited by the igniter element.

United States Patent [191 Hantack [111 3,826,605 July 30, 1974 [5'41 DIRECT BURNER IGNITION SYSTEM [75] lnventori Melvin E. Hantack, St. Louis, Mo.

[73] Assignee: Eaton Corporation, Cleveland, Ohio [22] Filed: Aug. 16, 1972 [21] Appl. No.: 281,067

[51] Int. Cl. F23n 5/00 [58] Field of Search 431/66, 67

[56] i References Cited I UNITED STATES PATENTS 3,454,345 7/1969 Dyrc 431/66 3,502,419 3/1970 7 Perl..,.... 431/66 3,597,139 8/1971 Elders 431/66 FOREIGN PATENTS OR APPLICATIONS 687,097 5/1964 Canada 431/66 Primary ExamineF-Edward G. Favors Attorney, Agent, or Firm-Teagno & Toddy 57 ABSTRACT A fuel igniter element having a resistance value which varies inversely as a function of element temperature is mounted proximate to a burner outlet and is electri cally series connected to a substantially constant resistance heater element. The heating element is operable to actuate a thermal valve at a predetermined current heating value to provide fuel to the burner. The series circuit is switchably connected to an electrical power source which when applied heats the igniter element .to the fuel ignition temperature of the fuel used. At

this temperature, the lowered resistance of the igniter element allows the current flow to increase to the pre' determined current value thereby actuating the thermal valve. Upon actuation, the thermal valve allows fuel to flow from the burner which is thenignited by the igniter element.

18 Claims, 6 Drawing Figures PATENIED 3.826.605

SHEET 1 0F 2 l /Z0 VAC FUEL 1 /0 SUPPL y THE/8M. L

FIG!

/Z0 VAC 2a 3 I -/0 FUEL l/ 5 SUPPLY I "BACKGROUND OF THE INYENTION 1. Field of the Invention This invention relates generally to fuel ignition systems for valve controlled burners and particularly to direct ignition-systems using an igniter element which allows an increased current flow to actuate a thermal valve upon reaching an ignition temperature.

2. Description of the Prior Art Prior art burner ignition devices generallyfall into two categories, namely, indirect and direct ignition devices.

The indirect'ignition devices generally comprise pilot flame ignited burner'systems wherein a fluid filled thermoresponsive device is continuously heated by the pilot flame to a predetermined temperature at which main valve. Another drawback is that the pilot flame,

may be shifted from the thermocouple by an air draft or completely extinguished thereby preventing the main valve from opening in either case. Since the pilot flame is burning continuously a waste of fuel also resultsiwhen the main burner'is not to be actuated for extended periods'of time. t

Direct ignition systems are known which utilize electrical means for producing sparks to directly ignite fuel flowing from a burner. A timing circuit is used in conjunction with the spark ignition means to terminate fuel flow to the burner if the fuel is not ignited within a predetermined time. Some flame detection means are also required for indicating to the timing circuit whether the fuel has'been ignited or not. As such these systems are complicated and expensive and require extensive troubleshooting to determine the cause of any failure occurring therein Direct ignition systemsgare also known which utilize a glow coil or heater element which isheated to the fuel ignition temperature and which are operable to ignite the fuel flowing from the burner. In these systems, some type of flame detecting means is required to ter 'minate fuel flow should the heater element fail to ignite the fuel. The detecting means may comprise infra-red sensors of flame conductivity sensors along with their associated circuitry. Such a system is disclosed in US. Pat. No. 3,649,156 issued to Leonard E. Conner. It will be appreciated that such a system requiring separate flame igniting and flame sensing elements is complicated and expensive since extensive circuitry is required to'coordinate the igniting and sensing functions into an operative system. 7

SUMMARY OFTI-IE INVENTION In one embodiment of the invention a variable resistance means provides a first resistance value when at ambient temperature and a second resistance value when heated by connection to an electrical power source. Valve actuating means are electrically series connected to this variable resistance means and are operable to allow fuel to flow to a burner only-after the variable resistance means achieves the second resistance valve. i t i In another embodiment of the inventiona thermal valve is connected between a fuel supply and a burner to provide a flow of fuel to the burner in response to a predetermined current. Ignition means, having a resistance which decreases with increased temperature is mounted proximate to the burner to provide an element which attains the ignition temperature of thefuel in response to the same predetermined current. Series circuit means connect the thermal valve and the ignition means to a power source whereby current flow from the power source is operable to increase the temperature of the ignition means thereby decreasing the resistance of the series circuit and allowing thepredetermined current valve to be obtained in the'circuit.

In yet another embodiment of the invention a parallel electric circuit means is series connected with the ignition means to control a heat valve and a'solenoid valve in response to the ignition means attaining fuel ignition temperature. I t Y I 1 The series connection of the temperature ignition means with the valve or valves which control fuel flow to the burner in the above described embodiments provides a simple and inexpensive direct fuel ignition apparatus which assures that fuel flow will only occur when the ignition element is at the fuel ignition temperature. Therefore, thereis no requirement 'forany separate flame sensing devices or delay circuitry as the pres ent invention automatically provides electrical fail-safe operation.

It is, therefore, the main object of this invention to provide a simple and inexpensive direct ignition system which is'electrically fail-safe.

. ment, which follows hereinafter.

Another object of this invention is to provide a fuel valve actuating system which is operable to actuate a.

fuel valve in response to a predetermined resistance of a variable resistance means which is electrically connected to the fuel valve.

Another object of this invention is to provide a direct ignition system which allows fuel flow to a burner only upon an ignition element attaining a fuel ignition tem perature.

Another object of the invention is to provide a direct fuel ignition system which is operable to actuate a plurality of valves to provide fuel flow to a burner in response to an ignition element attaining a fuel ignition temperature.

These and other objects of the inventionwill become more apparent from the description of the drawings and the detailed description of the preferred embodi- BRIEF DESCRIPTION or THE DRAWINGS FIG. 1 is a schematic drawing of one series connected direct ignition system. I v

FIG. 2 is a schematic drawing of a series-parallel connected directignition system. I r

FIG. 3 is a sectional side view of a thermally actuated bimetal valve which may be used in conjunction with the circuits of FIGS. 1 and 2.

FIG. 4 is a top view of the bimetal portion of the thermally actuated valve of FIG. 3.

FIG. 5 is a graph of resistance of and current flow through the igniter element versus temperature of the igniter element. I

FIG. 6 is a graph of current in the series circuit of FIG. 1 versus time after connection to a 120 Volt A.C. power source.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings wherein FIG. 1 shows a 120 Volt A.C. power source connected across a pair of lines L, and L with a thermostat switch 18, a heater coil 16, a trim resistor potentiometer 20, an igniter 14 and a fuse 22 all electrically connected in a series circuit associated therewith. This series circuit provides a direct ignition system for a burner 10. Fuel flow to the burner is controlled by a thermally actuated valve 24 positioned in a conduit 26 between the burner 10 and a fuel supply.

The thermal valve 24 is positioned to be actuated by the heater 16 as is indicated by the dotted line 25 in a manner that will be described later, with reference to FIGS. 3 and 4. The igniter 14 is mounted proximately to the outlet of the burner 10 to allow the fuel from the burner 10 to flow directly onto the igniter 14 upon actuation of the thermal valve 24.

The operation of the circuit of FIG. 1 is best understood with reference to the graphsof FIGS. 5 and 6. A master control thermostat (not shown) is used to set a reference temperature towhich the thermostat switch 18 controls the burner flame to maintain the reference temperature setting. However, since this part of the circuit is conventional in the art it need not be illustrated for purposes of understanding the invention. The thermostat switch 18 closes and allows the voltage across lines L L to be applied to the series circuit connected therebetween. The resistances of the trim resistor 20, the fuse 22 and the heater coil 16 are selected to be negligible as compared to the initial resistance of the igniter. 1 The igniter; 14 is a negative slope thermistor which is composed of silicon carbide materials and exhibits a decreased electrical resistance with increased temperature. A typical resistance v. temperaturecurve for such an igniter is disclosed at FIG. 5. Such igniter s are readily available from the Carborundum Company of Niagara Falls, New York.

As is'seen in FIG. 5 the igniter 14 has a resistance of 240 ohms at the initial ambient temperature of 80F when the series circuit between L and L is first connected to the 120 Volt AC power source. The initial current flowing through the igniter 14 is approximately 0.45 amps and the line voltage is proportioned therefore between the igniter and remaining elements with a 108 VAC drop across the igniter l4 and 12 VAC drop across the remaining elements. The igniter 14 is heated by the current flowing therethrough and rises in temperature while exhibiting a corresponding decrease in resistance until the resistance starts leveling off, at approximately 1,600F, to an approximate valve of 38 ohms. Of course, as the igniter 14resistance decreases, the current in the series circuit between L and L increases, due to a decrease in total circuit resistance, until it also levels out to an approximate value of 3 amps.

The thermal valve, as shown in FIGS. 3 and 4, is preselected to allow fuel flow to the burner IO-Whenever a current of approximately 2.8 amps flows through the heater coil associated therewith. Since this current flow is only possible when the resistance of the igniter 14 is approximately 38 ohms and this igniter resistance is only possible when the igniter 14 is at 2,200F or greater, ignition of the fuel flowing from the burner 10 is thereby assured since fuels such as natural gas have an ignition temperature of approximately 1,600F.

Once the fuel flowing from the burner is ignited, the burner 10will heat the surroundings until the thermostat senses that the preselected temperature has been attained and will then open the switch 18 to terminate current flow and close the thermal valve 24 preventing further fuel flow to the burner 10. The igniter 14 is also disconnected from the power source by the switch 18 and cools'downto its initial temperature.

The trim resistor 20 is a manually adjustablepotentiometer by which resistance may be added to the circuit and the maximum current flowing therein minimized thereby. The circuit is protected by a fuse 22 which will open circuit in situations of excessive current flow in the circuit. I

The circuit outlined above is electrically fail-safe in that any malfunction of the component parts will not cause a hazardous condition of allowing fuel to flow without it being ignited by the igniter 14. Should an open circuit develop in either the igniter 14 or the heater coil 16 current flow to the thermal valve 24 would stop and the valve 24 would close to shut off fuel flow to the burner. Should a short circuit develop in the igniter 14, the fuse 22 would open circuit due to excessive currentflow and prevent current flow to the valve 24 shutting off fuel flow. If the heater coil 16 is short circuited current flow therein would stop and the valve 24 would shut off fuel flow even though the igniter was The thermal valve 24, as shown in FIGS. 3 and 4, has an inlet 46 connected to the fuel supply side of line 26. The fuel is communicated therethrough to a chamber 44 wherein it exerts its supply line pressure on a valve plug 50 to seal a passageway 38 extending through a seat body 42 of an adjustable seat assembly 36 threaded into a valve plate 48. An ambient compensated bimetal assembly 52 is connected to the plug 50 by having its top portion slide into a keyway 51 formed in a bimetal element 60. The bimetal has one end joined to a compensating bimetal element 58 by means known to those familiar with the art. The other end of the element 58 is joined to an electrically insulating terminal block 56 by means also known to those skilled in the art. The heater coil 16 is wrapped around the element 58 with its ends connected to electrical connecting terminals 54. The bimetal elements 58, 60 are preselected to provide a constant force on the valve plug 50 throughout a range of temperatures as long as both elements are at the same temperature. However, when the heater coil is activated by current flow therethrough, it raises the temperature of the element 58 above that ofthe element 60 to unbalance the force on the plug 50 and cause it to be lifted from the seat assembly 36. This lifting occurs at the preselected current flow of 2.8 amps through the heater coil 16, at which time the added force from element 58 is sufficient to overcome the compensating force of element 60 as well as that of the fuel line pressure acting on the plug 50. The seat assembly 36 may be adjusted up or down by appropriately threading the assembly 36 in the plate 48. An adjustment slot 40 is provided to facilitate this action. The adjustable seat assembly is adjusted to vary the preload on the bimetallic spring element 60. Varying the preload on the spring element 60 changes the point at which the element 60 begins to move when heated. Thus, for a given current in the element heating coil 16 and corresponding thermal deflection of element 60, thevalve can be calibrated open or closed, by adjusting the position of the seat in the valve body. The adjustable seat thus enables calibration of the valve after complete'assembly, by inserting a suitable tool as, for example, a screw driver through valve outlet 26. Furthermore, the novel adjustable seat feature of the valve eliminates the need for providing a seal for an ad justment means penetrating the valve body. When the plug 50 is lifted from the seat assembly 36 fuel flows through the passageway 38 into an outlet 34which communicates with the burner 10 side of the supply line 26 to supply fuel to the burner 10 thereby.

The time within whichspecific circuit actions take place are seen in the graph of FIG. 6. When the circuit is first connected to the 120 VAC power supply at time seconds a current of approximately 0.45 amps initially flows in the circuit and rises to approximately 2.8 amps within the next 13 secondsfThis is the minimal current which when maintained for a brief period of time will cause sufficientheat in the heater coil 16 to heat the bimetal 58 to open the plug 50. As indicated on the graph, the valve 24 opens to allow fuel flow to the burner 10 after approximately 21 seconds or 8. seconds after the current has attained the 2.8 amp minimal level. This time delay helps to further assure that the igniter 14 reaches the fuel ignition temperature.

Referring now to FIG. 2, wherein like parts are similarly designated-but with a prime attached, the'circuit shown therein is particularly adaptable to direct ignition of burners in clothes dryer applications. Atimer switch 32 is electrically series connected with a thermostat switch 18' and a dryer door actuated motor switch" 30. A two branch parallel circuit is connected between line L and the motor switch 30. An electromagnetic coil 29 is located on one branch and a heater coil 16' is series connected to an igniter l4'located in the second branch. The electromagnetic coil 29 activates the solenoid valve 28 as is indicated by dotted line 31.

Thermal valve 24 and the soldnoid valve 28 are both connected in line with the supply line 26 and fuel flow to the burner 10 occurs only when both valves 24 and 28 are open.

In operation, when the timer (not shown) is set for a certain time interval, the timer switch 32 closes. If the thermostat (not shown) senses the dryer temperature is lower than the preselected temperature the thermostat switch 18 will also close. If the door is closed the dryer motor will operate and close theswitch 30 to apply power to the two parallel branches to complete the circuit. Power applied through the heater coil 16 and igniter 14' will open the thermal valve 24 after a period of time when the igniter is at the fuel ignition temperature, as was explained previously with respect to FIG. 1. Power applied through'the electromagnetic Fuel will continue to flow to the burner until any one of the switches 32, 18, or 30 are opened. When either of the switches 32, 18, or 30 opens it stops current flow to heater coil 16 and coil 29 to immediately shut off valve 28 to stop fuel flow. Thus when the thermostat 10 (not shown) senses that thepreselected temperature has been attained in the dryer, the thermostat switch 18' opens and terminates current flow to the solenoid coil 29 shutting off valve 28 to terminate fuel flow. When the dryer door is opened, the dryer motor (not shown) is stopped and it in turn opens the switch 30 and terminates current flow to the coil29 shutting off valve 28 to terminate fuel flow. Similarly when the timing cycle of the dryer ends, switch 32 opens and terminates current flow to the coil 29 shutting off valve 28 to terminate fuel flow.

This circuit is also electrically fail-safe, as was explained with reference to the circuit of FIG. 1, since the added elements of the coil 29 and valve 28 also fail only in a non-hazardous manner. A short circuitof the coil 29 will prevent development of the requisite electromagnetic force therein and the valve 28 will remain closed. Conversely, an open circuit of the coil 28 will prevent the requisite current flow and the valve 28 will likewise remain closed.

Certain modifications and improvements will become obvious to those skilled in the art upon reading this specification. One of such obvious modifications and improvements would be to incorporate a flame loss override circuit to shut off the power to the direct igni- 35 tion circuit upon loss of flame from the burner. This would function as a secondary mechanical fail-safe circuit. It is the applicantsintention, therefore, that all such obvious modifications and improvements be included within the scope of his invention.

Having described the invention so as to enable one skilled in the art to practice it,

I now claim: 1. A direct ignition system for a fuel burner comprising: I

an electrical power source; variable resistance means for providing a first resistance value when at ambient temperature and a second resistance .value lower than said first resistance value, when heated by connection to said power source; first valve'means including thermal actuating means electrically series connected to said variable resistance means, and operable to actuate said first valve means to provide a flow of fuel to said fuel burner in response to said variable resistance means reaching said second resistance value; and,

second valve means fluidically in series with said first valve means, said second valve means including actuating means electrically in parallel with said thermal actuating means.

2. A system as claimed in claim 1 wherein said variable resistance means includes a thermistor having a resistance value which is inversely proportional to the 7 temperature of said thermistor. Y

3. A system as claimed in claim 1 wherein said first valve actuating means includes:

a bimetal valve plug operably associated with said first valve means and normally biased to prevent flow from said first valve means to said burner; and

constant resistance heating means, electrically connected to said power source and said resistance means, and operable to overcome the normally biased condition of said bimetal valve plug in response to said resistance means reaching said second resistance value.

4. A system as claimed in claim 1 including:

a thermostat switch series connected between said power source and said resistance means and operable to connect said resistance means to said power source in response to a predetermined temperature.

5. A direct ignition system for controlling the ignition and flow of fuel to a fuel burner comprising:

an electrical power source;

thermal valve means connected between a fuel supply and said burner and including actuating means connected to said power source and operable to provide flow of fuel to said burner in response to a predetermined current flow therein;

solenoid valve means fluidically in series with said thermal valve means, said solenoid valve means including actuator means operably connected to said power source to open said solenoid valve means in response to a predetermined current flow therethrough;

ignition means having a resistance which decreases with increased temperature mounted proximate to the outlet of said burner said ignition means includingan element having a fuel ignition temperature in response to said predetermined current; and

series circuit means, connecting said thermal valve and said ignition means to said power source for increasing the temperature of said ignition means thereby decreasing the overall resistance of said ignition means to allow said predetermined current to flow through said series circuit means.

6. A system as claimed in claim 5 wherein said element of said ignition means includes a negative slope thermistor.

7. A system as claimed in claim 5 wherein said series circuit means includes:

a thermostat switch for connecting said power source in response to a predetermined temperature;

a trimresistor connected to said ignition means for adjusting the current in said series circuit means; and

a limit fuse to provide an open circuit in response to a predetermined limit temperature.

8. A direct ignition system for a valve controlled fuel burner comprising:

an electrically actuated thermal valve connected between said fuel burner and a fuel supply;

a solenoid-actuated valve in line with said thermal valve;

means providing a fuel ignition element proximate to the outlet of said burner, said fuel ignition element reaching fuel ignition temperature in response to a predetermined current flow therethrough; and

parallel electric circuit means, operating said thermal 6 valve and said solenoid valve in response to a fuel ignition temperature'being presentin said fuel ignition element, for providing an immediate closing of 8 said solenoid actuated valve upon a loss of current flow in said parallel circuit means.

9. A direct ignition system as set forth in claim 8 including:

an electrical power source; a manual switch series connected to said parallel circuit means to control the connection of said electrical power source to said parallel circuit means and said fuel ignition element. 10. A direct ignition system as set forth in claim 9 wherein said fuel ignition element includes a negative resistance thermistor having a fuel ignition temperature when a predetermined current flows therethrough.

11. A directignitionsystem as set forth in claim 10 wherein said parallel circuit means includes a substantially constant resistance heater mounted to said-thermal valve to control the opening of said thermal valve in response to said predetermined current flowing through said resistance heater.

12. A system for igniting a fuel burner comprising: a. control valve means for supplying fuel to said burner, including i. thermal valve means having a first electrical valve actuating means associated therewith, and

ii. solenoid actuated valve means fluidicallyin se ries with said thermal valve means and having a second electrical valve actuating means associated therewith;

b. said first and second electrical valve actuating means operable upon passage of a predetermined electrical current flow therethrough to open the burner control valve means; and

c. igniter means electrically in series with said first valve actuating means, said igniter means having a first resistance value at room temperature, which first resistance is sufficient to prevent said predetermined current flow in said first valve actuating means, and upon onset of current flow therethrough, said igniter means heats to a predetermined ignition temperature at which temperature said igniter means has a second predetermined resistance value lower than said first resistance such that, upon said igniter means reaching said second resistance value, said predetermined current flows in said first valve actuating means for opening the burner control valvemeans and, upon said igniter increasing in resistance above said second value, said predetermined current is prevented from flowing to said first valve actuating means and said control valve means is closed.

13. The system defined in claim 12, wherein said first valve actuating means includes:

a. a bimetallic arm having one end fixed and the other end operably connected to said control valve means; and,

b. heating means operable to heat said bimetallic arm and warp same, said heating means being in series with said igniter such that said arm biases said thermal valve means closed when said heating means is at room temperature and said arm is warped to open said thermal valve means when said predetermined current flows through said heating means.

14. The system defined in claim 12, wherein said control valve means includes:

a. a movable poppet operatively connected to said first valve actuating means; and,

3,826,605 9 a 10 h b. an adjustable valve seat having said poppet in warped to open said thermal valve when said precontact therewith when said control valve is in the determined current flows through said heating closed position, said adjustable seat being movable 7 means; and, a with respect tosaid first actuating means to vary b, said thermally a tuated valve include the operating position at which said thermal valve 5 i, a ov bl poppet operably conne ted to aid bimeans opens in response to said predetermined metallic arm,

Current Q through Said fi actuating means ii. an adjustable valve seat having said poppet in 15. The system defined in claim 12, wherein said first Contact therewith when said thermal valve is in Valve actuatinsmeans inlPde$1 the closed position, said adjustable seat being a blmetalhc arm havmg one fixed and Ihe movable with respect to said bimetallic arm to other-end operably connected to said thermally acvary the operating position at which said thermal b tlhate d valve; and, b1 h d b n valve opens in response to said predetermined eating meansopera e to eat sar rmeta 1c arm current flow through heating means 'alld Said heating. means .being series 18. A direct ignition system for a fuel burner comwith said igniter such that said arm biases said therprising,

ma] valve closed when said heating means is at (a) an electrial power Supply.

room temperature and Sald arm is warped to open (b) control valve means operable to permit fuel flow said thermal valve when said predetermined current flows through said heating means. to said burner, said control valve means including 16. The system defined in claim 12, wherein said thermally actuated valve includes:

a. a movable poppet operatively connected to said first valve actuating means; and, b. an adjustable valve seat having said poppet in contact therewith when said thermal valve is in the 20 (i) thermal valve means,

ii. solenoid valve means fluidically in series on the fuel line with said thermal valve means;

electrical igniter means adjacent said burner and operatively connected to said power supply, said closed position, said adjustable seat being movable withrespect to said actuating means to vary the operating position at which said thermal valve opens igniter means including resistance means having an initial resistance upon onset of current flow therethrough and a subsequent substantially lower resistance upon heating to fuel ignition temperature such that at said ignition temperature a predetermined current flows through said resistance means; and

d. valve actuating means operatively connected to said power supply, to said valve means and to said ignition means, said actuating means being operable in response to flow of said predetermined current to open said valve means and operable to close series with said igniter such that said arm biases said valve means in response to current flow of less said thermal valve closed when said heating than said predetermined value.

means is at room temperature and said arm is 40 in response to said predetermined current flow through said actuating means.

17. The systemdefined in claim 12, wherein: a. said valve actuating means includes:

i. a bimetallic arm having one end fixed and the other end operably connected to said thermally actuated valve,

ii. heating means operable to heat said bimetallic arm and warp same, said heating means being in 

1. A direct ignition system for a fuel burner comprising: an electrical power source; variable resistance means for providing a first resistance value when at ambient temperature and a second resistance value lower than said first resistance value, when heated by connection to said power source; first valve means including thermal actuating means electrically series connected to said variable resistance means, and operable to actuate said first valve means to provide a flow of fuel to said fuel burner in response to said variable resistance means reaching said second resistance value; and, second valve means fluidically in series with said first valve means, said second valve means including actuating means electrically in parallel with said thermal actuating means.
 2. A system as claimed in claim 1 wherein said variable resistance means includes a thermistor having a resistance value which is inversely proportional to the temperature of said thermistor.
 3. A system as claimed in claim 1 wherein said first valve actuating means includes: a bimetal valve plug operably associated with said first valve means and normally biased to prevent flow from said first valve means to said burner; and constant resistance heating means, electrically connected to said power source and said resistance means, and operable to overcome the normally biased condition of said bimetal valve plug in response to said resistance means reaching said second resistance value.
 4. A system as claimed in claim 1 including: a thermostat switch series connected between said power source and said resistance means and operable to connect said resistance means to said power source in response to a predetermined temperature.
 5. A direct ignition system for controlling the ignition and flow of fuel to a fuel burner comprising: an electrical power source; thermal valve means connected between a fuel supply and said burner and including actuating means connected to said power source and operable to provide flow of fuel to said burner in response to a predetermined current flow therein; solenoid valve means fluidically in series with said thermal valve means, said solenoid valve means including actuator means operably connected to said power source to open said solenoid valve means in response to a predetermined current flow therethrough; ignition means having a resistance which decreases with increased temperature mounted proximate to the outlet of said burner said ignition means including an element having a fuel ignition temperature in response to said predetermined current; and series circuit means, connecting said thermal valve and said ignition means to said power source for increasing the temperature of said ignition means thereby decreasing the overall resistance of said ignition means to allow said predetermined current to flow through said series circuit means.
 6. A system as claimed in claim 5 wherein said element of said ignition means includes a negative slope thermistor.
 7. A system as claimed in claim 5 wherein said series circuit means includes: a thermostat switch for connecting said power source in response to a predetermined temperature; a trim resistor connected to said ignition means for adjusting the current in said series circuit means; and a limit fuse to provide an open circuit in response to a predetermined limit temperature.
 8. A direct ignition system for a valve controlled fuel burner comprising: an elecTrically actuated thermal valve connected between said fuel burner and a fuel supply; a solenoid actuated valve in line with said thermal valve; means providing a fuel ignition element proximate to the outlet of said burner, said fuel ignition element reaching fuel ignition temperature in response to a predetermined current flow therethrough; and parallel electric circuit means, operating said thermal valve and said solenoid valve in response to a fuel ignition temperature being present in said fuel ignition element, for providing an immediate closing of said solenoid actuated valve upon a loss of current flow in said parallel circuit means.
 9. A direct ignition system as set forth in claim 8 including: an electrical power source; a manual switch series connected to said parallel circuit means to control the connection of said electrical power source to said parallel circuit means and said fuel ignition element.
 10. A direct ignition system as set forth in claim 9 wherein said fuel ignition element includes a negative resistance thermistor having a fuel ignition temperature when a predetermined current flows therethrough.
 11. A direct ignition system as set forth in claim 10 wherein said parallel circuit means includes a substantially constant resistance heater mounted to said thermal valve to control the opening of said thermal valve in response to said predetermined current flowing through said resistance heater.
 12. A system for igniting a fuel burner comprising: a. control valve means for supplying fuel to said burner, including i. thermal valve means having a first electrical valve actuating means associated therewith, and ii. solenoid actuated valve means fluidically in series with said thermal valve means and having a second electrical valve actuating means associated therewith; b. said first and second electrical valve actuating means operable upon passage of a predetermined electrical current flow therethrough to open the burner control valve means; and c. igniter means electrically in series with said first valve actuating means, said igniter means having a first resistance value at room temperature, which first resistance is sufficient to prevent said predetermined current flow in said first valve actuating means, and upon onset of current flow therethrough, said igniter means heats to a predetermined ignition temperature at which temperature said igniter means has a second predetermined resistance value lower than said first resistance such that, upon said igniter means reaching said second resistance value, said predetermined current flows in said first valve actuating means for opening the burner control valve means and, upon said igniter increasing in resistance above said second value, said predetermined current is prevented from flowing to said first valve actuating means and said control valve means is closed.
 13. The system defined in claim 12, wherein said first valve actuating means includes: a. a bimetallic arm having one end fixed and the other end operably connected to said control valve means; and, b. heating means operable to heat said bimetallic arm and warp same, said heating means being in series with said igniter such that said arm biases said thermal valve means closed when said heating means is at room temperature and said arm is warped to open said thermal valve means when said predetermined current flows through said heating means.
 14. The system defined in claim 12, wherein said control valve means includes: a. a movable poppet operatively connected to said first valve actuating means; and, b. an adjustable valve seat having said poppet in contact therewith when said control valve is in the closed position, said adjustable seat being movable with respect to said first actuating means to vary the operating position at which said thermal valve means opens in response to said predetermined current flow through said first actuating means.
 15. The system defined in claim 12, wherein said first valve actuating means includes: a. a bimetallic arm having one end fixed and the other end operably connected to said thermally actuated valve; and, b. heating means operable to heat said bimetallic arm and warp same, said heating means being in series with said igniter such that said arm biases said thermal valve closed when said heating means is at room temperature and said arm is warped to open said thermal valve when said predetermined current flows through said heating means.
 16. The system defined in claim 12, wherein said thermally actuated valve includes: a. a movable poppet operatively connected to said first valve actuating means; and, b. an adjustable valve seat having said poppet in contact therewith when said thermal valve is in the closed position, said adjustable seat being movable with respect to said actuating means to vary the operating position at which said thermal valve opens in response to said predetermined current flow through said actuating means.
 17. The system defined in claim 12, wherein: a. said valve actuating means includes: i. a bimetallic arm having one end fixed and the other end operably connected to said thermally actuated valve, ii. heating means operable to heat said bimetallic arm and warp same, said heating means being in series with said igniter such that said arm biases said thermal valve closed when said heating means is at room temperature and said arm is warped to open said thermal valve when said predetermined current flows through said heating means; and, b. said thermally actuated valve includes: i. a movable poppet operably connected to said bimetallic arm, ii. an adjustable valve seat having said poppet in contact therewith when said thermal valve is in the closed position, said adjustable seat being movable with respect to said bimetallic arm to vary the operating position at which said thermal valve opens in response to said predetermined current flow through heating means.
 18. A direct ignition system for a fuel burner comprising: (a) an electrical power supply; (b) control valve means operable to permit fuel flow to said burner, said control valve means including (i) thermal valve means, ii. solenoid valve means fluidically in series on the fuel line with said thermal valve means; c. electrical igniter means adjacent said burner and operatively connected to said power supply, said igniter means including resistance means having an initial resistance upon onset of current flow therethrough and a subsequent substantially lower resistance upon heating to fuel ignition temperature such that at said ignition temperature a predetermined current flows through said resistance means; and d. valve actuating means operatively connected to said power supply, to said valve means and to said ignition means, said actuating means being operable in response to flow of said predetermined current to open said valve means and operable to close said valve means in response to current flow of less than said predetermined value. 